Surveillance systems, and the like, commonly utilize floodlights or illuminators, particularly at night, to illuminate areas under surveillance. Visible light is not always desirable because it can be seen with the unaided human eye. The term "illuminator" is often used to refer to a source of visible light; however, the term is used herein to refer to infrared radiators, as well. Infrared radiation is detectable with cameras and serves to illuminate the scene detected by the camera in the same way as visible light illuminates a scene to the human eye. For this reason, security systems have increasingly utilized infrared radiation to illuminate areas without signalling to those in the area that surveillance is taking place. Infrared radiation or illumination of this type is particularly advantageous when used with closed circuit television surveillance equipment. Conventional infrared floodlights of the lens or reflector type, typically utilize radiation filters located in front of the lens which absorb visible light and allow infrared radiation to pass.
Prior sources of infrared radiation operate at very high temperatures due to the amount of heat generated in the process. A significant amount of heat is absorbed by the radiation filters. A common problem with conventional infrared floodlights is that such devices typically overheat by absorbing heat not only in the filters, but also in the surrounding structure. In particular, lamps emitting a high proportion of infrared radiation are known to become exceptionally hot when confined within a small area such as a housing. It is important to operate these lamps near their recommended operating temperatures. Higher than optimum temperatures reduce their life span. Thus, heat must be effectively dissipated in order to ensure that the device performs satisfactorily.
In an attempt to overcome this problem, some form of cooling is generally required to dissipate heat generated by the lamp. A variety of systems have been proposed to do so in order to prevent thermal damage to system components and permit more convenient handling and use of the illuminator. One such system employs a cooling fan to draw filtered exterior air through an opening in the housing, pass the air directly over the lamp and allow the resulting warm air to exit through another opening.
Although prior cooling systems remove some heat, they have not been successful in keeping the housing of an infrared illuminator within acceptable temperature limits during extended use. The high temperatures reached by the housing and other portions of such devices continue to pose a problem and have proven to be a hazard, especially during routine service and maintenance procedures. Any contact with the housing causes burns and excruciating pain.
An additional disadvantage associated with conventional infrared floodlights is that openings formed in the housing to admit and discharge exterior air allow visible light to escape. Measures to prevent visible light from escaping have resulted in the housing being tightly sealed. One existing system employs a seal surrounding the entire device and is configured such that the components of the housing are interlocked with one another. This proves to be a severe hindrance when servicing the device. For example, it takes time to disassemble the device, and once serviced, it is difficult and time-consuming to make sure that the unit is completely sealed again.
A need thus exists for an infrared illuminator or a source of infrared radiation which is configured to effectively dissipate heat and prevent visible light from leaking out, and which is adapted to simplify routine service and maintenance procedures.